Oscillation generator



June 18, 1940. J. F. FARRINGTON OSCILLATION GENERATOR Filed May 17, 1937 Q 3:350 uc A 524%? 653mm. @2530:

o o o ma ATTOR N EY Patented .June 18, 1940 UNITED STATES OSCILLATION ennnmron John F. Farrington, l luahing,- N. Y., assignor to Hazeltine Corporation, a corporation 'of Dela.-

ware

Application May 17, 1937, Serial No. 143,075

6 Claims.

This invention relates to oscillation generators and, particularly, to generators of oscillations of example, rooms with hard walls, floors, and

ceilings, reflection of the sound waves sets up interference patters and stationary waves. These interference patters shift with frequency. Under such conditions, if a microphone or corresponding device of the apparatus is disposed in a fixed position in the chamber, this position may be such that a satisfactory recording is not obtainable. For example, a microphone may be located at a node of a stationary wave of a particular frequency so that it gives no response thereto.

Various solutions of the foregoing problem have heretofore been suggested, but they have not been completely satisfactory. In certain cases the microphone has beencontinuously moved about the fixed position to integrate the sound energy. In accordance with a more satisfactory solution, however, the generator has been designed to develop audio-frequency oscillations normally at the desired pre-determined frequency, but cyclically deviating about this frequency, so that the undesirable effects mentioned above are avoided and a satisfactory recording of the sound wave of the average frequency propagated, ordinarily the predetermined frequency, is obtained. For this purpose it is essential that .the'

the high-frequency oscillations is adjusted to provide the required adjustment of the audio-frequency signal over the range, while the frequency of the other is cyclically varied to produce the desired deviations in the audio-frequency signal. The audio-frequency deviations in kilocycles, therefore, tend to be constant over the tunin range of the generator rather than a constant percentage of any selected audio frequency, which 6 latter is the desired relationship. Heretofore, this desired frequency deviation has been ob.- tained approximately by means of relatively complicated switching arrangements, whereby the effectiveness of the means employed for causing 10 these deviations has been adjusted in steps, providing different actual deviations for different component portions .of the audio-frequency range. Such arrangements, however, have required repeated and relatively complicated adjustments 15 and, moreover, have provided a control of the range of deviation only roughly approximating that required.

It is an object, therefore, of the present invention to provide an improved oscillation gen- 20 erator for generating oscillations normally at a predetermined frequency, but cyclically deviating about such frequency and including means whereby the range of the deviations may be readily ad- 1 justed. Y i

A further object of the invention is to provide an improved oscillation generator, embodying high-frequency oscillation generating means of the character described and an additional tunable high-frequency oscillation generating means, for 30 generating beat-frequency oscillations at any predetermined frequency within a wide range but cyclically deviating thereabout.

' A still further object of the invention is to provide an oscillation generator of the character last described, wherein cyclically deviating highfrequency oscillation generating means is automatically controlled in accordance with the tuning of the other high-frequency oscillation generating means, so that the range of deviations of 40 the beat-frequency oscillations is adjusted closely to approximate the same percentage ofthe' beat frequency for all beat frequencies within the range of the generator.

In accordance with the present invention,

there is provided an oscillation generator including an oscillation circuit for normally developing oscillations at a predetermined frequency. v The generator also comprises means including an auxiliary cyclically-tunable circuit coupled to the oscillation circuit to shift the resonant frequency. thereof, thereby to effect cyclical deviations of the oscillations from the predetermined frequency; There is further provided means for adjusting the coupling between the circuits to adjust the range of deviations without affecting the said predetermined frequency.

In one satisfactory embodiment of the invention, the oscillation generator comprises a first high-frequency oscillation generating means which is tunable over a predetermined range and a second high-frequency oscllation generating means normally developing oscillations at a fixed predetermined frequency, and means are coupled to these two generating means for deriving therefrom beat-frequency oscillations. Auxiliary means are associated with the second oscillation generating'mea'ns for effecting cyclic deviations from the predetermined frequency produced by it. Control means are arranged to adjust the effectiveness of the auxiliary means, thereby to adjust the range of the deviations. Unicontrol means are so connected as simultaneously to tune the first generating means and to adjust the control means at unequal rates and in a predetermined relation, thereby to adjust the range of the deviations substantially directly in accordance with the frequency of the first generating means as it is tuned over its tuning range.

For a better understanding of the invention,

together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a circuit diagram of a complete oscillation generator embodying the present invention; Figs. 2 and 3 are graphs representing certain operating characteristics of the generator of Fig. 1 to aid in the understanding of the invention; Fig. 4 is a side view, partially schematic, of unicontrolled tuning and variable inductance elements suitable for use in connection with the invention; and Fig. 5 is an end view of the variable inductance element of F18. 4.

Referring now more particularly to Fig. 1 of the drawing, there is shown schematically a beatfrequency oscillation generator embodying the present invention in a preferred form. In general, this generator includes a tunable high-frequency generator indicated generally at II and a fixed-tuned high-frequency generator indicated generally at I I. High-frequency bufler amplifiers l2 and Il are connected to the output circuits of the generators I. and II, respectively, and the output circuits of these amplifiers are, in turn, connected to a common input circuit of a modulator 14. The output circuit of the modulator may be connected through a beat-frequency amplifier IE to a sound-producing device or other utilization apparatus i6.

The high-frequency generators l0 and H are, in general, similar in construction and operation and corresponding elements thereof are desi nated on the drawing by similar reference numerals. The generator ll comprises an oscillation circuit l1 and a vacuum-tube oscillator It. The circuit l'l includes an inductance winding IS in parallel with an adjustable condenser 20. 'Series condensers 2| and 22 and series condensers 23 and 24 are connected across the-oscillation circuit, as shown. Condensers 2|, 22, 23, and 24 provide the main tuning capacitance for the circult ll, while adjustable condenser 20 provides the capacitance required to change the frequency of the circuit over a narrow range to vary the beat frequency over a wide range. The gridcathode circuit of tube It is connected across the condenser 22, a leak resistor 25 being connected between the grid of this tube and ground. The anode circuit of the tube l8 includes a feed-back winding 26 inductively coupled to the winding I 9. Operating voltage is supplied to the anode of the tube from a suitable source, indicated at +3, by way of a resistor 21 and the winding 26. A suitable high-frequency by-pass condenser 28 is provided to return the alternating plate current to the cathode. The input circuit of the high-frequency amplifier I2 is connected across condenser 24, as shown.

The high-frequency generator ll being, as stated above, of the same general construction as the generator ill, a detailed description of the parts thereof which are similar to parts of the generator I0 is unnecessary. For the purpose of clarity, the oscillation circuit of the generator II has been designated I111. The circuit Ha is not tunable so the condenser 20a, which corresponds to the adjustable condenser 20 of the circuit I1, is a fixed padding condenser adjustable only for aligning the circuit "a with the circuit [1 when the condenser 20 is at its minimum value. Further, in the circuit I'Ia there is provided a composite inductance element, corresponding to the winding iii of the circuit II, which includes the winding Isa and an auxiliary winding Mb. The generators l0 and II are preferably shielded, as indicated by the broken lines.

The system as thus far described is substantially conventional and its operation being well understood in the art, a detailed explanation thereof is unnecessary herein. Briefly, however,

oscillations are generated by the generator H at a fixed predetermined high frequency and by the tunable generator 10 at a different predetermined high frequency, preferably below the fixed frequency. These oscillations are then amplified in the amplifiers l2 and i3, which serve as buffer stages, and mixed in conventional manner in the modulator l4 to develop beat-frequency or audiofrequency oscillations. The beator audio-frequency oscillations are then amplified in the amplifier l5 and translated to the reproducer l6 or-other corresponding device for conversion into sound or other use.

Referring now more particularly to the portion of the'system embodying the present invention, there is provided in connection with the oscillation circuit ,I'Ia an auxiliary tunable circuit 30 comprising inductance windings 3| and 32, a resistor 33, and capacitance elements including the main frequency-determining condenser 35, which is adjustably fixed, and a relatively small adjustable tuning condenser 34. A suitable motor 31 is operably connected to the shaft of the condenser 34 for continuously adjusting the rotor of this condenser, thereby cyclically to vary the resonant frequency of the circuit 30 about its normal pre- 7 determined frequency, which is that of the circuit The winding 3| of circuit 3| is inductively coupled to the winding lab and arranged to provide therewith a variocoupler, indicated generally at 36, adjustable to vary the coupling between the circuits 30 and Na. Variocoupler 33 is preferably shielded from the other parts of the system, as indicated by the broken hues.

Unicontrol means, indicated by the broken line 38, are connected to the tuning condenser 2| of the oscillation circuit l1 and to the variocoupler 36 for simultaneously adjusting these elements, thereby to adjust the coupling between the auxiliary circuit 30 and the oscillation circuit [1a in accordance with the frequency to which the oscillation circuit I] is tuned. Preferably an indicator 39 and a dial 40 are provided in connection with the unicontrol means, the dial being calibratedi for example, 0-10,000 cycles, corresponding to the beat or audio frequencies developed by the system for various settings of the unicontrol means which adjusts the tuning condenser 20.

In the assembly of the system, the oscillation circuit I1 is preferably initially adjusted to develop; its maximum frequency, for example, 120 kilocycles, the tuning condenser 20 providing its minimum capacitance and the indicator 39 being at 0 on the dial 40. With the variocoupler .36 adjusted to provide substantially zero coupling between the circuits 30 and Ha, the circuit "a is adjusted to have the same resonant frequency as the oscillation circuit I! by adjusting condenser 20a. Obviously, with both of the highfrequency generators I0 and II developing oscillations at the same frequency no beator audiofrequencyoscillation is developed'by the modulator N and the output of the system is zero. The circuit 30 is next so adjusted that, with its tuning condenser 34 at its intermediate or mean position, it .is resonant at the same frequency as the circuit Ila. The maximum coupling provided by variocoupler 36 is limited to such a value that, under this condition, the circuit 30 has no effect on the resonant frequency of the circuit "a. Under certain conditions the circuit 30 reflects or introduces reactance into the circuit Fla and thereby shifts the resonant frequency thereof.- The amount of reactance so introduced depends mainly upon two factors: (1) the difference between the resonant frequency of the circuit 30 and that of the circuit "a, as controlled by adjustment of the condenser 34, and (2) the amount of coupling between these circuits, as controlled by the adjustment of the variocoupler 36.

In the operation of the system, the motor 31 rotates the shaft and the rotor of the condenser 35 and thereby causes cyclic deviations of the resonant frequency of the circuit 30 above and below its normal value, which is also that of the circuit l'la. With any appreciable coupling between the circuits, reactance is introduced into the circuit fla from the circuit 30 during these deviations, thereby causing corresponding deviations of the resonant frequency of the circuit Ha. The range of the deviations in frequency of circuit l'la depends upon the coupling between the circuits Fla and 30, and this range may be controlled by adjusting the variocoupler 36.

Adjustments of the condenser. providing the frequency deviation of the circuit 30 with respect to its mean resonant frequency effect corresponding frequency deviation of the circuit Ha, but thesedeviations are substantially linear with respect to the condenser adjustment only within predetermined limits. More particularly, this relationship holds -'only so long as the series reactance of the circuit 30, at the resonant frequency of the circuit I la, is less than its re- .sistance, or well within the limits providingthe linear relationship. In the preferred arrangement, the circuitconstants are such that the ratio of reactance of the inductance elements to .the resistance of the circuit 30 is relatively high at the resonant frequency of this circuit.

In order to obtain satisfactory results in the use of the system in acoustic testing, it is essential that the deviation of the beator audiofrequency signal developed be approximately the same percentage of its average frequency for all frequencies within the audible range of the system. A desirable deviation of the audio-frequency oscillations has been found to be :5% of thenormal or predetermined frequency plus some constant low frequency of the order of 5 or 10 cycles. The additional constant component of the frequency deviations is effective to break up the tent of these deviations in cycles is independent of the tuning of generator l0 to.vary the beatnote frequency. In order, therefore, to obtain the approximately uniform percentage deviation of the beat frequency over the entire tuning range of the generator, there are provided .unicontroi adjusting means 38 for the condenser 20 and the variocoupler, as described above. The unicontrol means 38 serves so to adjust the variocoupler 33, as the condenser 20 is adjusted over its range, as to increase the coupling between the circuits Ila and 30 and thus increase the beat-frequency deviations as the frequency of the high-frequency generator I 0 is decreased to increase the beatnote frequency developed in the modulator H.

In order that the increase in beat-frequency deviations bear the desired relation tothe average or normal frequency of the beat notes, the several elements of the system may be proportioned as follows: For convenience, the rotor plates of the condenser 20 are preferably so shaped that there is a relation between angular displacement and the resonant frequency of the circuit I1 such that the beat frequency between generators l0 and II is substantiallylogarithmically related to the rotational angle of condenser 20. For ideal results, the rate of adjustment of the variocoupler is generally different from that of the adjustment of the tuning condenser 20 and this may, of course, be accomplishedin any suitable manner. For example, this may be accomplished by utilizing a reduction gear between the unicontrol elements which operate the condenser 20 and the variocoupler and by including in series with the fixed winding of the variocoupler an auxiliary winding so proportioned and arranged as to effect the required difference in rate of coupling adjustment provided by the variocoupler 36 and capacitance adjustment provided by condenser 20. Such an arrangement is describecb hereinafter in connection with Figs. 4 and 5. 1

In order to aid in the explanation of the operation of the system described above, reference is made to Figs. 2 and 3. In Fig.2 curve A illustrates the relation between the frequencies developed by the generator l0 and the adjustment of the tuning condenser 20. Here the abscissae represent angular displacements of the rotor of the condenser 20 in degrees, and the ordinates represent resonant frequency of the circuit I1 in cycles. Obviously, the resultant beat frequency is thediiference between the fixed frequency of the generator II, for example, 120,000 cycles, and

the frequency developed by generator N, which ranges between 120,000 to 110,000 cycles. It will be seen from the curve A that a logarithmic variation of the beat frequency-is accomplished by the angular adjustment of the condenser rotor, this being due, as stated above, to the shape of the rotor plates.

In Fig. 3 there is shown a characteristic curve B illustrating the performance obtained by the system shown in Fig. 1 withv respect to the frequency deviation control. Here the abscissae represent the normal beat frequencies developed by the system and the ordinates represent the total range of frequency deviation, both in cycles. It is clearly shown by the curve B that for a low frequency, for example, 100 cycles, a range of deviation of approximately 20 cycles is obtained, while for a high frequency, for example, 10,000 cycles, a range of deviation of approximately 1,000 cycles is obtained. In other words, a deviation of approximately :5% of the audio frequency and cycles is obtained over the entire range.

While, in accordance with the present invention, any suitable mechanism, either electrical or mechanical, may be provided as the unicontrol device 38, one example of a mechanical unicontrol arrangement is illustrated in Figs. 4 and 5. According to this arrangement, the winding llb of the variocouples 30 comprises winding elements Ito and lid in series, rigidly secured to a fixed arm ll of a support 42, while the windin ii is mounted on a movable member 43. A shaft 44 is rotatably mounted in the support 42 and the member I: is rigidly'secured thereto, so that, upon rotation of the shaft, the Windingv 3| may be adjusted between a position coaxial with the winding lQc providing a maximum coupling and a position, as shown in Fig. 5, with its axis displaced from, but parallel to. the axis of the winding lid, providing a minimum coupling.

The auxiliary winding lid serves to vary the rate of adjustment of the coupling as the wind- An operating knob is, having an indicator a mounted thereon, is secured to one end of the shaft 44 and a gear 40 is secured to its opposite end. The rotor 20a of the tuning condenser 20 is secured to one end of a shaft 41, having a gear a secured to its opposite end in mesh with the gear 40. These gears are so proportioned that rotation of the shaft 44 effects rotation of the shaft 41 and, hence, adjustment of the condenser 20 at a predetermined greater'rate than that of the variocoupler, thereby, in cooperation with the shape of the condenser rotor and the variocoupler arrangement described above, providing the desired frequency deviation at different frequencies of the tuning range of the generator, as illustrated in Fig. 3.

While there has been described what is at present considered ,to be the preferred embodimerit of this invention, it will be obvious to those skilled'in the art that various changes and modifications may be made therein without do parting from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An oscillation generator including an oscillation circuit for normally developing oscillations at a predetermined frequency, means including an auxiliary cyclically tunable circuit coupled to said. oscillation circuit to shift the resonant frequency thereof, thereby to effect cyclic deviations of said oscillations from said predetermined frequency, and means for adjusting the coupling between said circuits to adjust, the range of said deviations without aflectin said predetermined frequency.

2. An oscillation generator including an oscillation circuit normally developing oscillations at a predetermined frequency, means including an auxiliary tunable circuit coupled to said oscillation circuit and having a mean resonant frequency equal to said predetermined frequency, means forcyclically tuning said auxiliary circuit to shift the resonant frequency of said oscillation circuit and thereby to effect cyclic deviations of said oscillations from said predetermined frequency over a relatively narrow range, and means for adjusting the coupling between said ,auxiliary circuit and said oscillation circuit to adjust the range of said deviations without affecting said predetermined frequency.

3. An oscillation generator including an oscillation circuit normally developing oscillations at a predetermined frequency, means including an auxiliary cyclically tunable circuit inductively coupled to said oscillation circuit to shift the resonant frequency thereof,. thereby to effect cyclic deviations of said oscillations from said predetermined frequency, and means for adjusting the inductive coupling between said circuits to adjust the range of said deviations.

4. An oscillation generator comprising a first oscillation generating means tunable over a predetermined range, a second oscillation generating means including an oscillation circuit normally developing oscillations at a predetermined frequency, means including an auxiliary cyclically tunable circuit inductively coupled to said oscillation circuit for shifting the resonant frequency thereof, thereby to effect cyclic deviations of said oscillations form said predetermined frequency, control means for adjusting the inductive coupling between said circuits to adjust the range of said deviations, means coupled to said two generating means for deriving therefrom beat-frequency oscillations, and unicontrol means for simultaneously tuning said first generating means and adjusting said control means, thereby to adjust said range of deviations as said first generating means is tuned over its tuning range.

5. An oscillation generator comprising a first oscillation generating means tunable over a predetermined range, a second oscillation generating means including an oscillation circuit normally developing oscillations at a predetermined frequency, means including an auxiliary tunable circuit coupled to said oscillation circuit and having a mean resonant frequency equal to said predetermined frequency, means for cyclically tuning said auxiliary circuit to shift the resonant frequency of said oscillation circuit, thereby to effect cyclic deviations of said oscillations from said predetermined frequency over a relatively narrow range. control means for adjusting the effectiveness of aaidtuning means and unicontrol means for simultaneously tuning said first generating means and adjusting said control means at unequal rates and in a predetermined relation to adjust said range of deviations sub stantially directly in accordance withthe frequency of said first generating means as it is tuned over its tuning range.

6. An oscillation generator comprising a first oscillation generating means tunable over a pre- 10 determined range, a second oscillation generating means for normally developing oscillations'at a predetermined frequency, auxiliary means for eflecting cyclic deviations of said oscillations from said. predetermined frequency, control means for adjusting the effectiveness of said auxiliary means to adjust the range of said deviations, means coupled to said two generating means for deriving therefrom beat-frequency oscillations, control means for tuning said first generating means, and unicontrol means for simultaneously adjusting said two control means at unequal rates and in a predetermined relation to adjust said range of deviations substantially directly in accordance with the frequency of said beat-frequency oscillations as said first generating means is tuned over its tuning range.

JOHN F. FARRIN'GTON. 

